This invention relates to mixing apparatus and more particularly to a new and improved continuous mixer which is capable of mixing a plurality of liquid ingredients in accurately maintained proportions, together with air, in a highly effective manner, to form a product of exceptional uniformity.
In manufacturing operations, it is often necessary to mix a plurality of liquid ingredients in accurately maintained proportions in order to make a desired product. For example, rigid polyurethane foams are made by interacting isocyanate and polyol in specified proportions in suitable mixing apparatus. Although attempts have been made heretofore to automate such processes by controlling the pumps supplying the ingredients to the mixer in response to sensed flow rates of the ingredients and specified values, the results have not been satisfactory. Such systems as have been devised have been based on analog signal control and have lacked the very high degree of accuracy and resolution required. Also, they have not been able readily to accommodate changes in throughput without substantial readjustment, and they have either been slow or unstable in effecting necessary corrections in flow rates as required.
It is an object of the invention, accordingly, to provide new and improved automatic continuous mixing apparatus that is substantially free from the above noted deficiencies of the prior art.
Another object of the invention is to provide new and improved mixing apparatus of the above character that is capable of maintaining the ingredient flow rates at specified values to a high degree of accuracy and resolution.
A further object of the invention is to provide new and improved mixing apparatus of the above character which is adapted to effect necessary corrections in ingredient flow rates in a rapid and stable manner.
Still another objective of the invention is to provide new and improved mixing apparatus of the above character in which the throughput can be adjusted without requiring separate adjustment of the set-in ingredient flow rates.
Yet another object of the invention is to provide new and improved mixing apparatus of the above character which includes means for rapidly detecting unfavorable or hazardous operating conditions and promptly signalling their existence to an operator, and, in case no remedial action is taken within a predetermined time interval, for automatically initiating remedial action if required.